As a packaging method of an acoustic wave device, there has been known a method that face-down mounts a chip including an acoustic wave element, and covers the periphery of the chip by a sealing member. Japanese Patent Application Publication No. 2008-546207 (Patent Document 1) describes that two substrates each including an acoustic wave element formed on the surface thereof are bonded together through an interlayer so that the acoustic wave elements face each other across an air gap.
The acoustic wave device can be downsized by forming acoustic wave filters on different surfaces and stacking them. However, the acoustic wave filters interfere with each other, and thereby, the isolation characteristic deteriorates.